Safety lockout for engine clutch

Abstract

Pneumatic actuation of an over-center clutch by a main control valve and fluid motor in the direction to engage the clutch is prevented by one or more safety lockout control valves each diverting the pneumatic pressure fluid from the main control valve to actuate the fluid motor in the direction of clutch disengagement while connecting the main control valve to drain. A single operative fluid pressure is employed.

I claim: 
     
       1. In combination with a mechanical drive clutch of the over-center type actuated by a double acting pneumatic piston-cylinder means supplied with pneumatic pressure from a source of such pressure through a main control valve selectively pressurizing either end of the cylinder, a remote safety lockout valve connected in the supply line from the source to the main control valve to provide for selective interruption of the pneumatic pressure to said main control valve, conduit means from said lockout valve to supply pneumatic pressure to the end of the power cylinder actuating the piston therein in a direction to disengage the clutch during said interruption of pneumatic pressure to said main control valve, means assuring exhaust of pneumatic pressure from the opposite end of the power cylinder during said selective actuation of said lockout valve, and means responsive to the pneumatic pressure from said lockout valve to prevent exhaust of pneumatic pressure through said control valve from said first named cylinder end. 
     
     
       2. The combination of claim 1 in which said last named means comprises a shuttle valve having a plunger alternatively movable to close either said conduit in response to pneumatic pressure from said control valve or to close the line from said control valve in response to pneumatic pressure from said conduit and in either instance to pass pneumatic pressure to the first named end of the cylinder to assure disengagement of the clutch. 
     
     
       3. The combination of claim 2 and a second lookout valve connected to selectively interrupt the pneumatic pressure from the source to the control valve, conduit means from said second lockout valve to said first conduit to supply pneumatic pressure to said first named cylinder end when said second lockout valve is selectively actuated, and a shuttle valve at the juncture between said conduits to alternatively close either of said conduits leading from the corresponding lockout valves when the other conduit is pressurized. 
     
     
       4. The combination of claim 1 in which a plurality of like lockout valves are employed with the pressure fluid output of each interconnected through shuttle valve means to isolate the actuation of any valve from the other valve or valves.